An inverse free-electron-laser accelerator

Recent work at BNL on electron acceleration using the Inverse Free-Electron Laser (IFEL) has considered a low-energy, high-gradient, multi-stage linear accelerator. Experiments are planned at BNL´s Accelerator Test Facility using its 50-MeV linac and 100-GW CO₂ laser. We have built and tested a fast-excitation wiggler magnet with constant field, tapered period, and overall length of 47 cm. Vanadium-Permendur ferromagnetic laminations are stacked in alternation with copper, eddy-current-induced, field reflectors to achieve a 1.4-T peak field with a 4-mm gap and a typical period of 3 cm. The laser beam will pass through the wiggler in a low-loss, dielectriccoated stainless-steel, rectangular waveguide. The attenuation and transverse mode has been measured in waveguide sections of various lengths, with and without the dielectric. Results of 1-D and 3-D IFEL simulations, including wiggler errors, are presented foe several cases: the initial, single-module experiment with ΔE=39 MeV, a four-module design giving ΔE=100 MeV in a total length of 2 m, and an eight-module IFEL with ΔE=210 MeV